The authorities will review the product safety requirements of personal mobility devices (PMDs), such as e-scooters, which currently do not need to be certified compliant before being sold here.

This was announced by Spring Singapore and the Land Transport Authority (LTA) in a joint statement yesterday, in response to queries from The Straits Times about a rising number of such devices catching fire.

Between January and September, the number of such fires rose to 31, up from 19 in the same period last year. The two most recent fires took place last week.

Experts have said that cheap batteries, which tend to be of inferior quality and to overheat, could have caused the fires.

"Unbranded" batteries can be bought for as little as $60, compared to batteries from reputable brands that cost up to five times more.

PMDs use mostly lithium-ion batteries. But as these batteries are subjected to high humidity, dust and vibration when used in PMDs, they have a higher chance of failure. Faulty or inferior quality batteries unable to stop charging when they are full also pose a fire risk.

Currently, safety guidelines for the use of PMDs cover only their weight, width and speed but do not cover batteries.

Spring Singapore and LTA did not indicate when the review will start or how long it will take.

Dr Soh Chew Beng, deputy director of the electrical power engineering programme at the Singapore Institute of Technology, suggested that battery packs be required to undergo electrical testing.

For example, an overcharge test will tell whether a battery pack will rupture or explode if there is overcharging. A temperature test will make sure the component cell batteries are able to maintain their operating currents, voltage and temperature limits during charging.

Mr Lim Biow Chuan, who is on the Government Parliamentary Committee for Transport, said he hopes the review will lead to PMDs being certified and registered with the authorities in the future.

"It'll be easier to track down devices that have been involved in accidents, or pose a risk to others," Mr Lim said.